Responding to an explosive newspaper report, Dank on Friday released a statement saying he consulted "with oncologists about what effects peptides would have on his (Mannah's) condition".

Mannah died from Hodgkin's lymphoma in January this year, aged 23.

He had recovered from a first bout of the lymphoma in 2009 to play the first five NRL matches of 2011.

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News Ltd newspapers on Friday published a leaked extract from an independent report commissioned by Cronulla into alleged use of peptides in the club's supplements program in 2011.

It questioned whether Mannah's cancer relapse could be linked to peptide use.

"I feel terribly sorry for what the Mannah family is going through right now. I can't imagine their pain," Dank said in a statement to the Nine Network.

"I'm outraged at the suggestion that I accelerated or contributed to his death.

"I was aware of what Jon's condition was. I definitely did not put him in a position where he could be harmed.

"I checked with oncologists about what effects peptides would have on his condition. I was assured they were safe for him to use.

"Like all players, Jon was given full information about what he was doing and it was his decision whether or not to take part.

"What has been reported and implied today is horrifying and untrue. My lawyers will follow this up in the strongest possible way."

Earlier on Friday, Parramatta co-captain Tim Mannah expressed his family's disappointment at reports linking his brother's cancer battle with alleged peptide use at the Sharks.

Serious doubts also emerged on Friday about the link between peptide use and the increased likelihood of a relapse or onset of lymphoma.

Leading cancer expert Professor Robert Baxter described the link as "tenuous at best".

According to Baxter, children undergoing treatment for leukaemia are occasionally treated with growth hormones to help give them normal growth.

Professor Baxter described that process as "highly controversial" but stressed there was no evidence that there was any risk - and pointed out peptide injections would promote even less potential risk.

"That's when the link is getting totally tenuous," Professor Baxter, from the Kolling Institute, at Sydney's Royal North Shore Hospital, told AAP.

"You could then say that theoretically this growth hormone could then make the body produce insulin-like growth factors and they could stimulate the cancer growth.

"It's a very long bow to draw, a really a tenuous link and a theoretical argument you could construct.

"But I'm saying there is no evidence that it's a genuine risk."

That provided little relief for the grieving Mannah family, with Tim forced to defend his late brother's integrity.

"On behalf of my family, I would like to say how disappointed we all are by the reports that have been published today," he said.

"My brother Johnny was a wonderful man and never, ever would have knowingly consented to taking a banned substance.

"In fact, he was very careful about everything he did that may affect his health.

"Johnny's integrity in the way he lived his life speaks for itself.

"We have no need to defend that."

The Sharks' world was turned upside after they were caught up in the investigation into the use of prohibited substances by the Australian Sports Anti-Doping Authority (ASADA) in February.

The Sharks were implicated due to their connection with Dank, who worked briefly with the club in 2011.